Meeting Abstract
More than 20 years have elapsed since Folstad and Karter introduced the Immunocompetence Handicap Hypothesis (ICHH), which proposes that honesty of androgen-dependent traits is enforced by the obligatory suppressive effects of testosterone (T) upon immune function. The ICHH has been tested mostly in temperate-breeding bird species, and support for the ICHH is mixed. Arctic-breeding birds provide a unique opportunity to investigate the ICHH because some species exhibit behavioural insensitivity to T at different stages of breeding. For example, T implants increase song, but not aggression in Lapland longspurs (Calcarius lapponicus) when females are incubating. We hypothesized that immunosuppression from T would also be blunted during this time, and therefore, not obligatory. Male longspurs were captured in Barrow, Alaska (71° N), placed in captivity, and implanted under the skin with silastic implants (20 mm) filled with testosterone or empty (control). T implants reduced cell-mediated immune responses to phytohemagglutinin (PHA), but not primary humoral responses to keyhole limpet hemocyanin (KLH), compared with controls. Baseline glucocorticoids were also elevated in T-implanted birds relative to controls, which suggests that stress hormones could be mediating immunosuppression. To support a role for indirect mediation by stress hormones, another group of males received corticosterone implants (12 mm) or control (empty) and then cell-mediated immunity was assessed. Corticosterone suppressed cell-mediated responses to PHA compared with controls. Despite exhibiting behavioral insensitivity to T, Lapland longspurs display T-induced immunosuppression similar to previous findings in temperate-breeding birds.
